1. Field of the Invention.
This invention relates in general to data storage systems, and more particularly to a method and apparatus for providing linear position (LPOS) estimations.
2. Description of Related Art.
Data loss is a serious threat to companies of all sizes, and catastrophic data loss can destroy a business. But most data loss isn""t the result of a big disaster, it""s caused by human error, viruses, and disk malfunctions. A suitable backup routine provides the best protection against data loss of all kinds. And tape technology remains the most efficient and cost-effective means to perform system backup, whether for a small business or a global 24xc3x977 operation.
Tape remains unrivaled in terms of cost and capacity for data storage, and should play an increasing crucial role in corporate data protection strategies. No other technology offers the same combined low cost and high capacity advantage of tape. While other technologies may offer strengths in one or more areas, overall, they do not meet the entire set of customer needs that tape addresses.
Tape drives make backup fast, easy, reliable and affordable. Speed is critical because your data is constantly growing while the time available for backup is shrinking. Even the slowest tape drive writes 1 MB per second and the fastest 30 MB per second, which means a 200 GB backup can be completed in less than two hours. Furthermore, unlike other storage methods, tape drives offer a range of media that allows you to back up all the data on a small to medium-sized server. Tape backup also captures system setup information, as well as data, allowing an entire system to be restored in the event a disaster strikes. Also, backups can be scheduled to occur automatically at a time determined to be most convenient.
Another area where tape storage excels is when it comes to data protection. Tape has proved itself a reliable medium, and tape drives themselves have never been more reliable. Easily portable, tapes have the added advantage of being simple to remove and store offsite, so keeping a disaster recovery copy is less of a burden.
In terms of affordability, tape is the most cost-effective way to store large amounts of data per gigabyte of storage. The compact size of tape cartridges also helps keep down your storage costs.
Nevertheless, the tape industry has become fragmented the proliferation of formats and technologies has overly complicated customer buying decisions. Therefore, LTO Technology (or Linear Tape-Open Technology) has been developed to combine the advantages of linear multi-channel bi-directional tape formats in common usage today with enhancements in the areas of timing-based servo, hardware data compression, optimized track layouts and high efficiency error correction code to maximize capacity and performance.
The new LTO tape product uses a tape format that has longitudinally pre-written servo tracks. The servo tracks provide a timing-based track-following position error system. The tracks contain a repeated pattern of recorded flux transitions that occur as grouped bursts of 5, 5, 4, and 4 transitions. The timing between the sets of 5-bursts and between sets of 4-bursts provides the position information for the track following system. Additionally, the individual transitions within the 5-bursts are phase-shifted in a manner that encodes longitudinal position information (LPOS) into the servo tracks. By detecting the phase-encoded LPOS information, the tape transport system determines the tape position relative to landmarks lengthwise down the tape. The LPOS information is used to keep track of the longitudinal position of data records written onto or read from the tape, and is used to locate those data records when the reading or writing process temporarily stops. The LPOS location of data files on tape is also stored in the volume control data for use to locate the data files during a later tape cartridge load for reading, or for write-appending new files onto the end of the last file written to the tape. The LPOS data is thus used as the primary positional information for the tape transport servo control system, it is used in the decision process for starting and stopping the tape, and for backhitching the tape in order to position the read-write heads at the beginning of a data record at the required velocity and track position which allows the start of a new data transfer operation.
Ideally the LPOS information from the servo track would be available all the time. In fact, it is only available when the servo read heads are positioned over the servo tracks, and tape speed is sufficient to produce read signal with servo read bias on, and the servo track is free of defects. When the LPOS from tape is unavailable, it must be estimated from other sources. The conditions when LPOS is not available from the servo track includes acceleration and deceleration of tape to velocity, indexing the servo read heads between servo bands, initial acquisition of the servo track during cartridge load and initialization, lateral recovery of the track following system to the servo tracks on tape, and defects in the servo read signal timings that make LPOS undetectable. All of these cases are common conditions in the normal operation of an LTO tape drive and require a regular and reliable method to estimate the LPOS data.
Accordingly, it can be seen that there is a need for a method and apparatus for estimating LPOS which always provides LPOS data, has sufficient accuracy to move tape over the whole tape length, and allows rewind and unload of the media.
However, during the read process, the tape transport system must synchronize the data channel to the media position to start the read data flow. For the first record to be read after the tape has been stopped, the tape transport system requires accurate LPOS information read from the tape in order to synchronize the read process to beginning of the data record on tape. This is normally done by requiring that valid LPOS data be read from tape. However, in very rare cases, there may be a defect in the servo read signal that makes LPOS invalid at this point. The result of this can be a permanent read error unless a second method of estimating LPOS very accurately is devised.
Therefore, there is a need for a method for, not only estimating LPOS which always provides LPOS data, has sufficient accuracy to move tape over the whole tape length, and allows rewind and unload of the media, but also for estimating LPOS so as to overcome a permanent read error which may occur due to mis-detected LPOS at the beginning of the first data record to be read after a tape stopped condition, repositioning condition, or a band change.
To overcome the limitations in the prior art described above, and to overcome other limitations that will become apparent upon reading and understanding the present specification, the present invention discloses a method and apparatus for providing linear position (LPOS) estimations.
The present invention solves the above-described problems by selecting a method for estimating LPOS based upon whether a read error prevents detection of valid LPOS values.
A method in accordance with the principles of the present invention includes a) determining whether detection of accurate and valid linear position data from a magnetic recording tape is needed, b) performing linear position estimation using the Hall effect sensors when linear position data from a magnetic recording tape is not needed and c) invoking an error recovery procedure to provide accurate and valid linear position information from tape when linear position data from a magnetic recording tape is needed.
Other embodiments of a method in accordance with the principles of the invention may include alternative or optional additional aspects. One such aspect of the present invention is that the accurate linear position information is synchronized to a validly detected linear position data from tape.
Another aspect of the present invention is that the accurate linear position information which is synchronized to a validly detected linear position data from tape within about one meter prior to the desired data record.
Another aspect of the present invention is that performing linear position estimation using the Hall effect sensors further includes i) scanning a media position trace in a media position trace table beginning with the most recently detected linear position, ii) subtracting a previous stored linear position from a most recent linear position, iii) determining whether the difference between the previous stored linear position and the most recent linear position is equal to 1, iv) using the most recent table entry to initialize the estimator when the difference is equal to 1, v) determining whether all eight entries of the media position trace table are exhausted when the difference is not equal to 1, vi) incrementing to a next most recent linear position when all eight entries are not exhausted and repeating ii-iii, vii) repeating ii-vi until a difference between successive linear position entries of 1 are found or all eight entries are exhausted, viii) using the value for linear position and Hall counter at LP2 when all eight entries are exhausted without finding a valid entry with which to initialize the linear position estimator, ix) loading value of inboard reel radius at LP2 and x) setting an estimate flag is set TRUE to enable the estimate computations and to replace the detected linear position from tape with the estimated linear position when the detected linear position from tape is invalid and the estimator is initialized.
Another aspect of the present invention is that an algorithm to estimate linear position from the Hall counter is given by the equations: linear position.estimate is the linear position(0)+(pi/Nhall)*[Rad+Rad(0)]*[HallCountxe2x88x92HallCount(0)], where, linear position.estimate is the estimated linear position, linear position(0) is the initial condition for linear position, Rad is the radius of the inboard reel, Rad(0) represents the initial condition for inboard reel radius, HallCount represents the inboard motor hall counter value, HallCount(0) represents the initial condition for the inboard hall counter, pi is a physical constant, and Nhall represents the resolution of the hall sensors.
Another aspect of the present invention is that invoking an error recovery procedure further includes reading linear position from tape when a tape transport system has locked onto a servo track prior to a data record to be read and when the velocity is controlled to a predetermined velocity, begin estimating linear position by measuring time intervals since the last valid linear position detected when valid linear position is lost prior to reaching the target data record, counting the servo interrupt timings, accumulating to a value equal to the number of interrupts between nominal linear position detection points, resetting the accumulator to zero when this value has been reached, incrementing the linear position estimate if tape motion is forward, and decrementing the linear position estimate if tape motion is backward, determining whether the estimated target linear position is reached, and the data flow synchronized and when the estimated target linear position is not reached, or the data flow is not synchronized, counting the servo interrupt timings again until the estimated target linear position is reached or the data flow is synchronized.
Another aspect of the present invention is that the predetermined velocity error is less than 0.5 percent of the nominal value of 4 meters/second.
In another embodiment of the present invention, a tape drive is provided. The tape drive includes magnetic recording tape having servo signals and data recording thereon, tape takeup and supply reels for spooling the magnetic recording tape thereon, a head for reading signals on the magnetic tape, reel motors, coupled to the tape takeup and supply reels, for driving the tape takeup and supply reels to move the tape relative to the head, Hall effect sensors, coupled to the reel motors, for sensing revolution of the tape takeup and supply reels, the Hall effect sensors providing a Hall count resolution for linear tape position that varies with tape reel radius, a controller for driving the reel motors and an estimator, coupled to the Hall effect sensors, for using the Hall count to produce linear tape position information, wherein the estimator scans a media position trace in a media position trace table beginning with the most recently written linear position, subtracts a previous stored linear position from a most recent linear position, determines whether the difference between the previous stored linear position and the most recent linear position is equal to 1, uses the most recent table entry to initialize the estimator when the difference is equal to 1, ascertains whether all eight entries of the media position trace table are exhausted when the difference is not equal to 1, increments to a next most recent linear position when all eight entries are not exhausted and repeating the subtracting and determining, repeating the subtracting, determining, using and ascertaining until a difference between successive linear position entries of 1 are found or all eight entries are exhausted, uses the value for linear position and Hall counter at LP2 when all eight entries are exhausted without finding a valid entry with which to initialize the linear position estimator, loads a value of inboard reel radius at LP2 and sets an estimate flag is set TRUE to enable the estimate computations and to replace the detected linear position from tape with the estimated linear position when the detected linear position from tape is invalid and the estimator is initialized.
In another embodiment of the present invention, a tape drive is provided. The tape drive includes magnetic recording tape having servo signals and data recording thereon, tape takeup reels for spooling the magnetic recording tape thereon, a head for reading signals on the magnetic tape, reel motors, coupled to the tape takeup reels, for driving the tape takeup reels to move the tape relative to the head, Hall effect sensors, coupled to the reel motors, for sensing revolution of the tape takeup reels, the Hall effect sensors providing a Hall count resolution that varies with tape reel radius, a controller for driving the reel motors and processing signals from the head, and an estimator, coupled to the Hall effect sensors, for using the Hall count resolution to produce linear position information, wherein the estimator reads linear position from the tape when a tape transport system has locked onto a servo track prior to a data record to be read and when the velocity is controlled to a predetermined velocity, begins estimating linear position by measuring time intervals since the last valid linear position detected when valid linear position is lost prior to reaching the target data record, counts the servo interrupt timings, accumulates to a value equal to the number of interrupts between nominal linear position detection points, resets the accumulator to zero when this value has been reached, increments the linear position estimate if tape motion is forward, and decrementing the linear position ed if tape motion is backward, determines whether the estimated target linear position is reached, and the data flow synchronized and when the estimated target linear position is not reached, or the data flow is not synchronized, counting the servo interrupt timings again until the estimated target linear position is reached or the data flow is synchronized.
In another embodiment of the present invention, an article of manufacture comprising a program storage medium readable by a computer is provided. The medium tangibly embodies one or more programs of instructions executable by the computer to perform a method for providing linear position (LPOS) estimations, wherein the method includes a) determining whether detection of accurate and valid linear position data from a magnetic recording tape is needed, b) performing linear position estimation using the Hall effect sensors when linear position data from a magnetic recording tape is not needed and c) invoking an error recovery procedure to provide accurate and valid linear position information from tape when linear position data from a magnetic recording tape is needed.
Another aspect of the article of manufacture of the present invention is that the accurate linear position information is synchronized to a validly detected linear position from tape.
Another aspect of the article of manufacture of the present invention is that the accurate linear position information which is synchronized to a validly detected linear position from tape within about one meter prior to the desired data record.
Another aspect of the article of manufacture of the present invention is that performing linear position estimation using the Hall effect sensors further includes i) scanning a media position trace in a media position trace table beginning with the most recently written linear position, ii) subtracting a previous stored linear position from a most recent linear position, iii) determining whether the difference between the previous stored linear position and the most recent linear position is equal to 1, iv) using the most recent table entry to initialize the estimator when the difference is equal to 1, v) determining whether all eight entries of the media position trace table are exhausted when the difference is not equal to 1, vi) incrementing to a next most recent linear position when all eight entries are not exhausted and repeating ii-iii, vii) repeating ii-vi until a difference between successive linear position entries of 1 are found or all eight entries are exhausted, viii) using the value for linear position and Hall counter at LP2 when all eight entries are exhausted without finding a valid entry with which to initialize the linear position estimator, ix) loading value of inboard reel radius at LP2 and x) setting an estimate flag is set TRUE to enable the estimate computations and to replace the detected linear position from tape with the estimated linear position when the detected linear position from tape is invalid and the estimator is initialized.
Another aspect of the present invention is that an algorithm to estimate linear position from the Hall counter is given by the equations: linear position.estimate is the linear position(0)+(pi/Nhall)*[Rad+Rad(0)]*[HallCountxe2x88x92HallCount(0)], where, linear position.estimate is the estimated linear position, linear position(0) is the initial condition for linear position, Rad is the radius of the inboard reel, Rad(0) represents the initial condition for inboard reel radius, HallCount represents the inboard motor hall counter value, HallCount(0) represents the initial condition for the inboard hall counter, pi is a physical constant, and Nhall represents the resolution of the hall sensors.
Another aspect of the article of manufacture of the present invention is that invoking an error recovery procedure further includes reading linear position from tape when a tape transport system has locked onto a servo track prior to a data record to be read and when the velocity is controlled to a predetermined velocity, begin estimating linear position by measuring time intervals since the last valid linear position detected when valid linear position is lost prior to reaching the target data record, counting the servo interrupt timings, accumulating to a value equal to the number of interrupts between nominal linear position detection points, resetting the accumulator to zero when this value has been reached, incrementing the linear position estimate if tape motion is forward, and decrementing the linear position ed if tape motion is backward, determining whether the estimated target linear position is reached, and the data flow synchronized and when the estimated target linear position is not reached, or the data flow is not synchronized, counting the servo interrupt timings again until the estimated target linear position is reached or the data flow is synchronized.
Another aspect of the article of manufacture of the present invention is that the predetermined velocity error is less than 0.5 percent of the nominal value of 4 meters/second.
These and various other advantages and features of novelty which characterize the invention are pointed out with particularity in the claims annexed hereto and form a part hereof. However, for a better understanding of the invention, its advantages, and the objects obtained by its use, reference should be made to the drawings which form a further part hereof, and to accompanying descriptive matter, in which there are illustrated and described specific examples of an apparatus in accordance with the invention.